This invention relates generally to a method for gamma irradiating products in a consistent reproducible manner to eliminate potential biological contaminants while maintaining biological activity, and specifically to a method which allows for a precise mapping of the dosage of gamma radiation delivered to the product throughout the carrier. Dose maps provide the manufacturers of biological material the information required to ensure that each of the product containers in a carrier receives an amount of radiation that falls within an acceptable range.
Biological products have validated specifications for inactivation treatment by gamma radiation. These biological products must be irradiated on dry ice in polyfoam containers to protect the product integrity. The polyfoam container insulates the product and the dry ice while maintaining temperatures at or below the validated specified range. Considerable amounts of energy and thus heat are generated during the irradiation process, temperatures typically exceed 10.degree. C. to 15.degree. C. above ambient. This temperature range is deleterious to the biological product.
Additionally, the bottle/product container configuration within the box significantly affects the amount of radiation penetration to the actual product. The greater the density, the lower the amount of penetration or delivered dose. It is the irradiation received at each point that allows for inactivation of bacteria, fungi, mycoplasma, bacteriophage and viral contaminants. Therefore, specific validated bottle configurations have been determined to maximize radiation penetration to all bottles within the polyfoam containers. These configurations enable a more uniform distribution of radiation, thus reducing the minimum to maximum radiation dose throughout the product. An additional factor to consider is placement of the shipping boxes on carriers. Carriers are used to bring the shipping boxes to the radiation source. These irradiation conditions must be emulated in the dose mapping procedures.
Dose mapping is a method whereby manufacturers of biological products are able to predetermine an amount of radioactivity received at a specific point in a carrier. New dose maps are required each time an irradiation parameter is changed. For example, each time the box, i.e., box configuration, bottle type, carrier configuration, or the source of radiation is changed, a new dose map is required. These dose maps are performed on product irradiation models that emulate irradiation conditions without using a product in the system. In these systems it is of vital importance that all parameters are identical to actual product irradiation conditions. If all the parameters, such as density and product positioning, are not identical to product irradiation conditions, the dose map will not be an effective way to establish a protocol whereby each product container receives an amount of radiation that falls into a specific range. This range is important because if the amount of radiation received is below a predetermined amount there would be inadequate inactivation of adventitious agents and if the amount of radiation received is above a predetermined amount, the product will lose biological activity.
There is one main reason why dose mapping is not done on actual product. Dosimeters, which are used to measure the amount of radioactivity, do not give accurate data in cold conditions, less than -20.degree. C. Since the dosimeters cannot be used in cold conditions, any product used would be destroyed. Thus it would be a waste of resources to use product for dose mapping. Therefore, a method is needed whereby manufacturers of biological materials are able to determine the amount of radiation at a specific point in an irradiation model designed to emulate product irradiation conditions. The closer the test conditions are to actual irradiation conditions, the more precise the dose mapping will be, thus allowing a proper range of radioactivity to be delivered to each product container.
The reason dosimeters do not give proper readings in cold conditions is because the kinetics of the chemical reaction are enhanced which would ultimately lead to under exposure of the product and incomplete inactivation. During irradiation dry ice is used to maintain the integrity of the product. Therefore, to emulate product irradiation conditions, a dry ice substitute is required for dose mapping experiments. A dry ice substitute requires approximately the same shape and density as dry ice so that the same amount of radioactivity reaches the dosimeters in the dose map system as would under product irradiation conditions. Dry ice pellets have a density of approximately 0.785 g/ml.
One known substitute for dry ice includes the use of dog food with salt pellets combined in a ratio of 5.2 pounds of dog food with 4.8 pounds of salt pellets. Dog food has a density of 0.4596 g/ml. Therefore, one problem with dog food is that it does not have a density similar to dry ice. In addition to the density, the dog food has a shape different from dry ice. Dry ice is 13/8.times.3/4.times.1/2" and the dog food is 5/8.times.5/8.times.3/8". Therefore, the density and shape of dog food made it an inadequate substitute. Additionally, dog food was too brittle for repeated use which increased the cost of dose mapping. Therefore, there is a need for a dry ice substitute that more closely emulates dry ice and that does not lose its shape over time.
In addition to the need for an effective dry ice substitute, dose map systems would be more effective if the dosimeters could be fixed into the center of the product container so that an accurate reading at the exact center of the product container could be recorded. Biological product or other liquids are not effective for dose mapping for several reasons. For example, a liquid will not fix the dosimeter into a center position. In a liquid, the dosimeter will float around making an accurate reading of the exact center of the product impossible. Another reason for needing an improved medium is that current mediums (saline solution) do not have a density similar to the product, thereby reducing the chance of obtaining a true dose map. Lastly, fiscal responsibility requires the use of a cheap and effective product substitute.
One product that manufacturers currently expose to radiation is animal serum. Animal serum and animal proteins derived from serum are essential supplements required for the growth of most cells in vitro. Serum is indispensable in the production of biologicals for animal and human pharmaceutical markets. It has the encumbrance of possible contamination by adventitious agents. At best, this leaves pharmaceutical manufacturers open to failed production runs and, at worst, introduction of a viral contaminant in the final product.
In addition to quality control, appropriate testing of all animal-derived raw materials is required in the manufacture of pharmaceuticals. The Code of Federal Regulations, Title 9,.sctn.113.53, requires the testing of serum products by serial passage in susceptible cell lines for the determination of viral contamination. This test is inadequate for detecting low levels of contamination in serum products. Typically, most production scale lots of serum are 1,000 liters. A 45 ml sample of serum is generally all that is required for Title 9 testing. Assuming a viral titer of one viable particle per liter of serum, the chance of obtaining a contaminated particle in any test sample is less than four percent (4%).
Currently, several manufacturers are utilizing gamma radiation as a treatment for potential contamination. Gamma radiation is the preferred treatment method due to its effective inactivation, lack of residuals, lower lot-to-lot variation, and it is minimally intrusive. Although, currently it is difficult to map the exact amount of radiation received at any particular point in the carrier, due to the high density of the product along with void spaces between the product container, it is impossible to guarantee the specified delivered dose without knowing the precise amount of radiation being received at these individual places inside a carrier. The density variation makes it possible to have portions of the product receive too much radiation and other portions not receive adequate amounts of radiation. The former possibly degrading the biological material, and the latter allowing possible contamination due to ineffective inactivation of adventitious agents.
Thus, current techniques for measuring the amount of radiation at a specific point in a carrier are inadequate to allow a realistic dose map to be created. For example, current techniques do not allow a proper determination of the amount of radiation received at the very center of a product container. Even if a dosimeter could be fixed to the center of a container, the density will not be the same as when product is in the container. Thus, current systems will not emulate actual irradiation conditions. Additionally, the current dry ice substitute lacks the proper parameters to emulate dry ice effectively. Therefore, a method is needed whereby dosimeters can be fixed to the center of a product container, product containers are filled with a material having a density similar to that of the product to be irradiated, and an effective dry ice substitute placed in the shipping box to eliminate void spaces between the product containers and the shipping box.
The above method is needed to comprehensively dose map carriers to ensure that all areas of the carriers receive a dose of radiation within a specified range, such that there is significant contaminant reduction without compromising product performance.